A conical burner comprised of several jackets, a so-called double-cone burner, is known from EP 0 321 809 B1. The conical swirl generator comprised of several jackets generates a closed torque stream, which becomes unstable due to the increasing torque in the direction of the burner outlet opening, and is transformed into a ring-shaped torque stream with a reverse stream in the core. The jackets of the swirl generator are composed in such a way that tangential air inlet slots are formed for combustion air along the burner axis.
Supplies for premix gas, i.e. the gaseous fuel, are provided on the inflow angle of the cone jackets on these air intake slots, which have outlet openings for the premix gas distributed along the direction of the burner axis. The gas is jetted in through the outlet openings, or bores, respectively, lateral to the air intake slot. This jet combined with the torque of the combustion air/fuel gas stream created in the torque space leads to a good mixture of the fuel or premix gas with the combustion air. A good mixture is a prerequisite in these premix burners for low NOx values during the combustion process.
As a further improvement of such a burner, a burner for heat generation is known from EP 0 780 629 A2, which in addition to the swirl generator, has an additional mixing course for the further mixing of fuel and combustion air. This mixing course can, for example, be embodied as a down streamed tube section, into which the stream leaving the swirl generator is transferred without any significant loss of stream. The degree of mixing can be further increased, and the emission of pollutants can therefore be reduced by means of the additional mixing course.
WO 93/17279 shows another known premix burner, in which a cylindrical swirl generator with a conical interior body is used. In this burner, the premix gas is also jetted into the torque space via supplies with respective outlet openings, which are arranged along the axially extending air intake slots. In its conical interior body, the burner additionally has a central supply for pilot gas, which can be jetted into the pilot area adjacent to the burner outlet. The additional pilot level serves for the startup of the burner and an expansion of the operating range.
Such premix burners are used particularly in modern natural gas-fired gas turbines for the reduction of nitrogen emissions (NOx). The burners operate at the operating point of the gas turbine, but also operate in the upper load range at part load operation at high firing temperatures. In order to maintain the NOx, emissions within certain limits, which are continuously being further tightened by legislators of many countries, the premix burners must be operated at a very lean operational mode near their quenching limits. In part, however, strong pulsations occur during this operating range, which may cause damage to the burner and the combustion chamber components of the gas turbine.
In order to avoid or reduce the pulsations, so-called passive measures are known which are used to change the pulsation behavior on the burner and in the combustion chamber. To some extent, however, these measures require massive changes, adjustments, or even new developments of the burner and the combustion chamber system.
A fuel injection system for a stepped gas turbine combustion chamber is known from DE 196 20 874 A1, in which the main burner is operated with pulsated fuel injection.
By means of a targeted selection of the pulsation frequency, the common combustion frequencies can be controlled with this technology in such a way that combustion pulsations can be reduced.
The pulsated injection of fuel is also utilized in the so-called active pulsation control method. In this method, the combustion pulsations are measured by means of a pressure sensor and analyzed. In case combustion pulsations occur that are too strong, a small part of the supplied fuel quantity is fed via a separate gauge, and supplied to the burner in a pulsated manner. The pulsation frequency is adjusted according to the highest peak amplitude of the measured combustion pulsations, but phase-delayed. The total fuel stream modulated in this way causes the combustion pulsations to be attenuated, and they are not able to self-increase, or swing back up. A disadvantage of the pulsated supply of fuel, however, is that gauges are required for the modulation of the fuel supply, which must be able to generate a modulation at a frequency from a few Hz up to several hundred Hz. But such gauges are exposed to substantial wear of the movable parts, and can therefore cause a failure of the gas turbine facility.
Based on this prior art, the task of the present invention is to provide a premix burner with improved flame stabilization, as well as a method for improved stabilization of the flame of a burner, which requires fewer assembly components that are prone to wear and tear.